This circuit was obtained in an American documentation from the 80's. The transistors can be equivalent to those indicated and the crystal can reach a few tens of megahertz.
With this circuit it is possible to simultaneously control two low voltage incandescent lamps. SCRs...
The OR function has the truth table shown next to the diagram in the figure. We have the output at...
High-brightness LEDs of various colors and even white can be obtained easily in specialized...